The present invention pertains to the art of molecular separation, specifically the physical separation of molecules in gaseous mixtures. The invention finds particular application in the separation of nitrogen from atmospheric air to provide a source of high concentration oxygen. In the preferred embodiment, the oxygen enriched gas is supplied at appropriate pressure, rate, purity, and the like for human respiration or other medical applications. The present invention is especially suited for providing oxygen to patients who require elevated concentrations of oxygen in their breathing air. It is to be appreciated, however, that the invention is also applicable to the separation of gaseous molecules of other types such as drying high purity gases, separating hydrogen from gaseous hydrocarbons or other hydrogen compounds, and the like.
A pioneer apparatus and method for fractioning gaseous mixtures by adsorption is illustrated in U.S. Pat. No. 2,944,627, issued July 12, 1960 to Charles W. Skarstrom. In the Skarstrom system, a cross-over valving assembly alternately channeled the gas to be fractionated to first and second vessels. The cross-over valve assembly further connected the vessel which was not receiving the gas with a waste gas discharge. The vessels were packed with a material, for example zeolite, which selectively adsorbed one or more components of the gas and passed an enriched product gas. The produce gas which passed through the vessel was channelled to a primary product outlet with a large fraction being channelled to the other vessel. The fraction flushed the adsorbed or waste gases which had been trapped by the other vessel. Cyclically, the cross-over valving assembly switched the connection of vessels with the incoming gas and the waste gas discharge. This cyclic switching of the vessels provided a regular flow of the primary product gas from the primary product outlet.
Numerous improvements have been made upon the Skarstrom system. One of these improvements is illustrated in U.S. Pat. No. 3,313,091 issued April, 1967 to Norton H. Berlin. The Berlin system utilized a vacuum pump to draw the adsorbed or waste gases from the vessel or bed which was being purged. Further, the Berlin system used a more complex valving system to produce a cycle which included vessel or bed pressure equalization (up), repressurization, product production, bed pressure equalization (down), dumping, and purging.
Among the patents which assert improvements upon the Skartstrom and Berlin cycles is U.S. Pat. No. 4,222,750 issued September, 1980 to William D. Gauthier et al. In the Gauthier system, the vessels or beds cyclically underwent 30 second periods of adsorption in which they received gas from a compressor and desorption in which they were connected with a vacuum pump. During at least a 20 percent but not more than 33 percent of the desorption cycle, i.e. 6 to 10 seconds, a portion of the primary product gas from the adsorbing bed was passed through the desorbing bed. This portion of the primary product gas flushed or purged the adsorbed gas products from the desorbing bed. With the disclosed timing cycle, Gauthier proported to achieve 95 percent oxygen purity at a flow rate of 2 liters per minute, dropping linearly to a 58 percent oxygen purity at 10 liters per minute.
One of the problems with the Gauthier cycle was that a portion of the primary product gas which was separated during adsorption was lost during purging. During purging, primary product gas was swept with the adsorbed gas through the vacuum pump and discharged to the atmosphere. This lowered the primary product gas production capacity and efficiency of the system.
The present invention contemplates a new and improved gas fractioning apparatus and method which provides improved primary product production capacity and efficiency.